The present invention relates to a jolt control for a drive system including a prime mover with an accelerator pedal, and an automatic transmission.
An automatic transmission is shiftable between two gear positions by hydraulically activating friction elements selectively. The quality of a shift operation in the automatic transmission may be evaluated by inspecting a waveform of the transmission output torque. FIG. 12 shows in the fully drawn curve a a waveform of the transmission output torque which induces a substantial shift shock during a gear shift operation with the throttle valve kept at a constant throttle opening degree.
It is proposed in Japanese Patent Application Kikai No. 58-77138 to reduce shift shock during a gear shift operation by reducing the output torque of the prime mover during a gear shift operation. This proposal is intended to reduce the peak of the transmission output torque during the gear shift operation for shock reduction by reducing the output torque of the prime mover. In FIG. 12, a dotted lines curve b shows a waveform of the transmission output torque during the gear shift operation where the proposal above is applied.
When the accelerator pedal is released to decrease the throttle opening degree TH, as shown in FIG. 11, in the course of the torque-down operation for shock reduction, however, a torque drop c occurs due to an additional prime mover torque reduction, inducing an additional shock owing to a difference between the bottom of this torque drop c and the transmission output torque obtained after the gear shift operation.
An object of the present invention is to improve a jolt control system of the above kind such that the occurrence of an additional shock of the above kind is suppressed.